As a method of manufacturing a piezoelectric resonator unit used in, for example, an oscillation device or a bandpass filter, the following method is known. For example, as described in Patent Document 1, a piezoelectric resonator unit is manufactured by mounting a piezoelectric resonator (such as a quartz crystal blank) on a substrate by using a conductive adhesive, performing frequency adjustment of the piezoelectric resonator so as to have desired frequency characteristics, and then hermetically sealing the piezoelectric resonator in an internal space by a recessed metal cover.
However, hitherto, for example, in a manufacturing process of sealing a piezoelectric resonator or in using a completed product, changes in physical properties of a conductive adhesive have occurred due to the humidity of the hermetically sealed internal space, as a result of which variations in frequency characteristics of the piezoelectric resonator unit sometimes occurred. Such variations in frequency characteristics occur after performing a frequency adjustment step for acquiring desired frequency characteristics, and the amounts of variations in frequency characteristics differ according to products and are difficult to predict. Therefore, it may be difficult to manufacture a piezoelectric resonator unit having desired frequency characteristics.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2012-191648